A general aim of this research proposal is to use diploid human somatic cells to study the intracellular regulation of growth. Fibroblasts from individuals with syndromes of growth retardation will be used to detect and anaayze factors that regulate growth. This study will also generate knowledge about the molecular basis of syndromes of retarded growth. The roles of cyclic nucleotides in the regulation of the cell cycle will be examined in synchronous cultures of normal and transformed cells.